During drilling operations for extraction of hydrocarbons, a variety of recording and transmission techniques have been attempted to provide or record real time data from the vicinity of the bit to the surface during drilling. The use of measurements while drilling (MWD) with real time data transmission provides substantial benefits during a drilling operation. For example, monitoring of downhole conditions allows for an immediate response to potential well control problems and improves mud programs.
Measurement of parameters such as location, environment, weight on bit, torque, wear, and bearing condition in real time provides for more efficient drilling operations. MWD techniques help achieve faster penetration rates, better trip planning, reduced equipment failures, fewer delays for directional surveys, and the elimination of a need to interrupt drilling for abnormal pressure detection.
Antennae, whether used for the transmission and reception of interrogating fields during logging operations or for the electromagnetic communication of data, can be delicate devices that cannot be too heavily shielded or they will not be able to perform their functions. Furthermore, antennae cannot be exposed to wellbore conditions, particularly during drilling operations, without substantial risk of harm or malfunction. Consequently, traditional antenna constructions for downhole use utilize solid wellbore tubulars, such as drill collar tubulars and drill pipe tubulars, to form a housing that protects the antenna from damage due to the corrosive fluids, high pressures, and high temperatures frequently encountered in wellbores particularly during drilling operations. Traditional techniques require that a portion of the tubular be “necked-down” during milling and/or machining operations by radially reducing the tubular at a particular location to provide a rather deep and wide groove. Typically, a layer of cushioning and electrically-insulating material is provided in the groove, and the antenna windings are wound about the tubular at the position of the groove to protect the antenna from physical damage and to allow communication of electromagnetic fields between the antenna windings and the borehole and surrounding formation. A slotted sleeve is typically provided and secured in position over the antenna windings provided within the necked-down portion of the tubular member.